1. Field of the Invention
The present invention relates to a grid moving method using a selective pixel search method and an apparatus using the grid moving method, and in particular, to an improved grid moving method using a selective pixel search method and an apparatus using the grid moving method which are capable of forming a grid with respect to an image of an object having a shape information and/or an image information, defining a unit region, moving the thusly formed grid, re-constructing an image grid, so that it is possible to reduce the number of blocks which are occupied by an object to be coded, thus significantly reducing the amount of computation and increasing a computation speed.
2. Description of the Conventional Art
Generally, in order to code a signal information of an object, a discrete cosine transform (hereinafter called DCT) and a vector quantizer are used. Recently, a shape adaptive DCT (hereinafter called SADCT) is used as a method for coding an object using a shape information of an object.
The above-described SADCT is directed to effectively coding a signal information of an object having a predetermined shape. Namely, an image frame is divided into blocks each having a predetermined size, thus coding only a signal information of the object.
Namely, when the block is filled with an information to be coded, the coding efficiency thereof becomes identical to a two-dimensional block DCT. When the block is not filled with an information to be coded, a one-dimensional DCT is processed with respect to the signals corresponding to the region of the object in the direction of a horizontal axis, and anther one-dimensional DCT is processed with respect to the results which are obtained after the previous one-dimensional DCT process in the direction of a vertical axis, thus thereby obtaining a final resultant value.
In addition, in the SADCT, a method of filling the block with as much as images of the objects can obtain more compression efficiency of a transform coefficient rather than dividing an image of an object into blocks based on the DCT coding gain.
Therefore, when performing the SADCT, the number of blocks within which the images of the objects to be coded is preferably reduced, thus coding the same.
In addition, when performing a conventional DCT or a block quantization, the coding is directly processed, thus increasing a bit ratio per frame and the number of blocks into which the images of the objects are occupied. Therefore, there is a predetermined limit for reducing the amount of signal information data.
Therefore, in order to overcome the above-described problems, the inventer of the present invention disclosed a method for adjusting a block position of the grid in accordance with the position of a target object and coding the same, thus thereby enhancing the coding efficiency.
It is possible to enhance the coding efficiency by reconstructing an image by moving the grid, estimating the motion of the object, and coding a texture information. In addition, the block grid is moved, and the start position is changed, so that the number of blocks corresponding to the objects is minimized. The above-described method is called as a shape adaptive region splitting method.
The above-described shape adaptive region splitting is used for a videophone, a teleconference, a personal communication system (PCS), a mobile phone, an advanced coding technique, etc. which are applicable using an MPEG-IV.
If there is provided an object, which is to be coded, in an image screen, a predetermined object or a certain region having a shape information is coded by the block unit on one screen.
Here, the unit of blocks is N.times.M, and a polygonal shape such as trigonal, hexagonal, etc. may be defined in one block.
Generally, if there is provided an object, which is to be coded, in an image screen, a shape adaptive region splitting is used with respect to a predetermined object or a certain region having a shape information.
For example, in the MPEG-IV, a VOP may be deemed as an object of the image screen.
The VOP is directed to separately coding an object by separating objects when there is provided an object in an image screen.
At this time, the horizontal and vertical values of a minimum image size of an object and an object information are transferred.
When performing the shape adaptive region splitting method, in the block-based coding process, in a state that the object is not moved, the grid is moved, and a grid start point is searched and coded so that the block having a minimum number of shapes of an object is formed, thus enhancing a coding efficiency.
FIG. 1 illustrates a VOP coding unit of a conventional VM (Verification Model) encoder. The VOP with respect to each object image formed by a VOP formation unit 10 is inputted into a motion estimation unit, thus estimating a motion by the unit of macro blocks.
The motion information estimated by the motion estimation unit 11 is inputted into a motion compensation unit 12, thus compensating the motion of the object.
In addition, the VOP the motion of which is compensated by the motion compensation unit 12 and the VOP formed by the VOP formation unit 10 are inputted into a subtractor 13, and a difference value therebetween is computed by the subtractor 13. The difference value computed by the subtractor 13 is inputted into an intra-object information coding unit 14, and the intra-object information is coded by the sub-block unit of the macro block.
The VOP the motion of which is compensated by the motion compensation unit 12 and the intra-object information coded by the intra-object coding unit 14 are inputted into an adder 15, the thusly inputted values are added by the adder 15. The output signal from the adder 15 is inputted into a previously reconstructed VOP 16, thus detecting a VOP of the previous screen.
The VOP of the previous screen detected by the VOP detection unit 16 is inputted into the motion estimation unit 11 and the motion compensation unit 12, respectively, and is used for a motion estimation and motion compensation.
Meanwhile, the VOP formed by the VOP formation unit 10 is inputted into the shape information coding unit 17, thus coding a shape information.
Here, the use of the output signal from the shape information coding unit 17 is determined based on an applicable field of the VOP coding unit. The output signal from the shape information coding unit 17 is inputted into the motion estimation unit 11, the motion compensation unit 12, and the intra-object information coding unit 14, respectively.
The motion information estimated by the motion estimating unit 11, the intra-object information coded by the intra-object information coding unit 14, and the shape information coded by the shape information coding unit 17 are multiplexed by a multiplexer 18 and then is transferred in a bit stream form through a buffer 19.
FIG. 2 illustrates a minimum size of square containing an object to be coded in a method of FIG. 1.
FIG. 3 is a view illustrating an object enlarged in the rightward direction and lowerward direction by the unit of a macro block size. The number of blocks within which the object is defined through a start point conversion by moving the block grid (dotted line).
FIG. 4 is an enlarged view illustrating a block A which is one of object boundary blocks of FIG. 3. The size of the block is 16.times.16. Here, the size of the same may be preferably 4.times.4. The size thereof is defined as N.times.M.
In the conventional art, a previous pixel of a block is searched in order to determined whether an object is defined within the block of FIG. 5.
For example, when the size of the block is 16.times.16, the maximum number of pixels is 256 in order to determined whether an object exists in the block.
Therefore, while the 256 pixels are being searched, even if one pixel is searched, the block in which the pixel exists is judged to be a block in which the pixel exists, and then the searching is performed with respect to the next block.
In addition, the entire blocks should be checked in order to determine whether an object exists in the block.
Therefore, in the conventional art, since it is verified whether an object exists in each block of the entire VOP while the block grid start point is being moved, the computation is repeatedly performed, and the computation speed becomes slow.
Namely, in the conventional art, since the entire pixels of the block should be checked in order to determine whether an object exists within a predetermined block, the computation speed becomes slow.